Vehicle engines commonly utilize cooling assemblies to remove excess heat from the engine and maintain an optimal operating temperature. The cooling assembly pumps a coolant through the engine and other components in order to control engine temperature. Heat generated within the engine and other components is absorbed by the coolant and dispersed into the surrounding atmosphere through the use of a radiator. In order to improve dispersal by the radiator, it is common to utilize fan assemblies to draw or force air past the radiator to assist in temperature transmission.
It is not always desirable for such fan assemblies to be run continuously. At times, it is desirable for the temperature within the coolant to increase rather than decrease. Additionally, continuous operation when unnecessary places an non-required draw on the engine and thereby reduces efficiency. To compensate for this, present fan assemblies utilize fan clutch assemblies that allow for the selective engagement of the fan to the engine such that the fans are engaged only when necessary. The fan clutch assemblies may be operated in a plurality of configurations including hydraulic and air-pressure actuated. It is common for these systems to be biased towards fan operation such that when failure occurs in the clutch assembly, the fan continuously operates to keep the engine cool.
Airactuated friction clutch assemblies of this type which work well for their intended purpose are found in U.S. Pat. Nos. 7,731,006, 7,055,668, and 7,430,956.
An issue with airactuated fan clutch assemblies relates to situations where the air pressure is too low to adequately cause actuation of the fan drive. This could result, for example, from a leak in the air supply, or a drain of pressure due to constant repeated usage. Without sufficient pneumatic pressure, the friction clutch might not engage solidly causing possible overheating and damage to the friction assembly and clutch.
It would therefore be desirable to have pneumatic clutch fan assembly with a system for protecting the fan assembly by preventing engagement of the friction clutch when a low pressure situation exists.
It would also be desirable to provide a clutch assembly with a pneumatic control mechanism that would prevent slip damage due to low, external operating air pressure.
It would further be desirable for such a clutch assembly to provide optimal performance and operation at all times during operation.